Fin-on-tube type heat exchanger



May 3, 1966 T. A. M GREW FIN-ON-TUBE TYPE HEAT EXCHANGER Filed April 17,1964 INVENTOR.

THOMAS A. McGREW BYW t-us ATTORNEY United States Patent M 3,249,156FIN-ON-TUBE TYPE HEAT EXCHANGER Thomas A. McGrew, Fern Creek, Ky.,assignor to General Electric Company, a corporation of New York FiledApr. 17, 1964, Ser. No. 360,606 3 Claims. (Cl. 165-181) The presentinvention relates to heat exchangers and is particularly concerned witha heat exchange coil of the fin-on-tube type comprising a plurality ofparallel tubular sections passing through a plurality of transverselydisposed parallel fins.

Heat exchangers of the fin-on-tube type employed, for example ascondensers or evaporators in refrigeration equipment comprise connectedparallel passes of tubing for conducting the refrigerant and a pluralityof thin metal fins which are designed to increase the heat transferbetween the refrigerant and the air passing through the heat exchanger.The design of a commercially acceptable heat exchanger requires theconsideration of a number of factors. The heat flow between the tubesand the fin structure is dependent upon the area contact of the finmaterial with the surfaces of the tube. In order to increase thiscontact and hence the heat transfer rate, the use of relatively thickand strong fin material and/or the bonding of the fin material to thetube by means of solder or the like is indicated. However, both thickfin materials and the soldering operation involve an increased cost ofthe heat exchanger. Also, it is not practical at present to usesoldering or brazing materials with aluminum fin stock. Heat transferbetween the fin material and the air circulated over the heat exchangeris a function more of fin surface area than fin thickness. Thereforewithin limits, it is desirable to use a relatively large number ofrelatively thin fins both for increasing the heat exchange area and alsofor limiting the material cost of the heat exchanger.

It is a primary object of the present invention to provide a new andimproved heat exchanger particularly characterized by an optimized finconstruction from the standpoint of cost and heat transfer requirements.Further objects and advantages of the present invention will becomeapparent from the following description and features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In carrying out the objects of the present invention, there is provideda fin-on-tube heat exchanger comprising a plurality of spaced finsincluding a plurality of spaced openings for receiving the tubecomponents of the heat exchanger. Each of the fins is corrugated overits entire area and the pattern of corrugations is designed to providemaximum strength in the fin material at the tube openings and in theremaining areas between the tube openings to facilitate manufacture ofthe heat exchanger. These results are obtained primarily by acorrugation pattern that provides continuous corrugations radiallyextending from one tube opening to each adjacent tube opening.

For a better understanding of the invention reference may be had to theaccompanying drawing in which:

FIGURE 1 is a general view of a fin-on-tube heat exchanger embodying thepresent invention;

FIGURE 2 is an enlarged view of a portion of the heat exchanger ofFIGURE 1 illustrating the corrugated fin pattern or structure of thepresent invention; and

FIGURE 3 is an edge view from line 3-3 of FIG- URE 1.

Referring to FIGURE 1 of the drawing, the illustrated fin-on-tube heatexchanger comprises tubing formed into a sinuous or serpentine shape toprovide a plurality of Patented May 3, 1966 parallel passes 1 connectedby return bends 2, each of the latter serving to connect two of thepasses. For a low cost, lightweight heat exchanger, the tubing ispreferably composed of aluminum as are also the fins 3 which areoperatively associated with the passes 1 in order to obtain a good heattransfer between the fins and the passes.

In accordance with the present invention, each fin 3 contains aplurality of openings 4, each of which is adapted to receive one of thepasses 1. These openings, as illustrated in FIGURE 2, are preferablyarranged in one or two parallel rows with the openings in each rowspaced from one another and spaced from the openings in the remainingrows. More specifically for two rows, the tube receiving openings 4 andhence the tube passes 1 contained within these openings are so arrangedthat the openings in one row are aligned with the openings in the otherrow or in other words, as viewed in FIGURE 2, the tube openings 4 in theupper row are directly above corresponding tube openings in the bottomrow.

This configuration of the tube openings within the fin 3 permits acorrugated pattern in the fins 3 which is designed to provide maximumstrength for the individual fins even though they may be made ofrelatively thin material, such as .005 inch aluminum sheet.

More specifically, while corrugated fin structures having variouscorrugation patterns have previously been used or proposed forstrengthening purposes or for the purpose of improving the heat transferbetween the fin surfaces and the air circulating over and between thefins, the fins of the present invention are characterized by acorrugation pattern which optimizes fin construction on the basis ofmaterial cost and strength and heat transfer requirements.

The fin of the present invention is shown in detail in FIGURES 2 and 3of the drawing illustrating a portion on one fin in which the tubeopenings are arranged in two parallel rows with the openings in one rowdirectly opposite the openings in the other row or, in other words, arearranged so that four adjacent openings comprising two from each row areat the four corners of a rectangle.

The corrugated pattern for the fins 3 is a repetitive pattern, the unitpattern of which is defined by the rectangle. The unit pattern includesa plurality of continuous corrugations extending radially from each tubeopening to the adjacent tube openings in the same row and in theadjacent row and this series of corrugations defining the perimeter ofthe unit pattern area encloses an inner area in which the fin materialis corrugated to provide a plurality of intersecting curved corrugationsdefining concentric rectangles having relatively concave sides.

More specifically, the fin material between any two adjacent tubeopenings is provided with one or more relatively straight corrugations 8extending radially from one tube opening directly to an adjacent tubeopening and a plurality of curved corrugations 9 and 10 of increasedcurvature which also extend radially from one tube opening and radiallyinto an adjacent tube opening. These continuous corrugations 8, 9 and 10between adjacent openings may be described as having substantially thesame shape and arrangement as the magnetic lines of force between unlikemagnetic poles. These continuous corrugations extending radially fromeach tube opening provide maximum pressure strength for the fin materialdefining the tube opening and thereby permits maximum pressure contactbetween the tube and fin material for good heat transfer properties.Also, as will be described more fully hereinafter, they provide maximumrigidity for the fin material between adjacent tube openings tofacilitate assembly of the fins and the passes 1 without distortion orbending of the fins.

The central area of the unit corrugation pattern, that is the areawithin the series of corrugations extending continuously from each tubeopening to an adjacent tube opening is also corrugated or rigidized by aplurality of interconnecting corrugations 11 and 12 defining concentricor rectangles having concave sides whereby these areas of fins 3 arealso strengthened.

Since the fins 3 are characterized by a repetitive pattern ofcorrugations, the corrugations such as 9a and 10a correspond tocorrugations 9 and 10 but terminate in the various edges of the finmaterial as indicated in FIGURE 3 of the: drawing while one or more ofthe corrugations such as 11 terminate as corrugations 11a in the edgesof the material. Thus the corrugations 9a, 10a, 11a and comparablecorrugations strengthen the edges of the fin material and permit the useof a thinner fin stock insofar as these areas are concerned.

Preferably the corrugated fins are manufactured by pressing fiat finstock between platens having surfaces designed to provide the desiredcorrugated patterns and at the same time or subsequently punching thefin openings 4 and the slots 14 connecting each of the openings to anedge of the fin stock. The purpose of the slots 14 is to permit assemblyof the tube passes 1 Within the openings 4 employing any of the wellknown means for accomplishing this result. For example, the passes 1 maybe flattened or made into an oval configuration of a dimension such thatthey can readily be inserted through the slots 14 and into the tubeopenings 4. Thereafter, either by hydraulic means or by applyingsuitable pressure to the exposed surfaces of the tube contained withinthe openings 4, the tube passes are pressed into a circularconfiguration and in tight engagement with the adjacent edges of the finmaterial defining the openings 4. In this process, the radiallyextending corrugations 8, 9 and 10 provide maximum fin strength in theseareas to resist any forces resulting from the deformation of the tubepasses 1 and thereby to provide an intimate contact between the finedges and the passes.

Alternatively the notches or slits 14 can be omitted and variousstraight pieces of tubing corresponding to the passes I inserted intothe openings 4 and thereafter connected by return bends to provide thefinished heat exchanger.

Due to the fact that a thinner fin material can be used when providedwith a corrugated pattern of the present invention, relatively low costheat exchangers can be produced using lightweight material such asaluminum. The overall irregular fin surface provided by the corrugationsalso provides for a greater heat transfer rate between the fin surfacesand the air circulated over the heat exchanger while the corrugatededges of the tube openings in contact with the passes 1 provide maximumcontact between the passes and the fins without use of solderingmaterials or the like. The continuous corrugations 8, 9 and 10 betweenthe various tube passes provides maximum rigidity in the fin structurefor resisting the pressures which may be applied to the passes 1 afterassembly in the openings 4 for the purpose of deforming these passesinto intimate engagement with the fin edges.

While the invention has been described with reference to a particularembodiment thereof it will be understood that it is not limited theretoand intended by the appended claims to cover all such modifications ascome within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A heat exchanger comprising a plurality of spaced fins each includingopenings for receiving the tube components of said heat exchanger,

said openings being positioned so that each set of four openings formthe four corners of a rectangle,

each of said fins having a repetitive pattern of corrugations oversubstantially the entire area thereof,

a unit pattern of said corrugations being defined by said rectangle,

said unit pattern including a series of corrugations extending radiallyfrom each of said openings and terminating in an adjacent opening.

2. A heat exchanger of the fin-on-tube type comprising a plurality ofspaced fins each including spaced openings for receiving the tubecomponents of said heat exchanger,

said openings being positioned whereby four of said openings form thefour corners of a rectangle,

a unit pattern of said corrugations being defined by said rectangle,

said unit pattern including a series of corrugations extending radiallyfrom each of said openings and terminating in an adjacent opening,

the central area of said unit pattern comprising a plurality ofintersecting curved corrugations defining concentric rectangles havingconcave sides.

3. A heat exchanger comprising a plurality of spaced fins each includingat least one row of spaced openings for receiving the tubular componentsof said heat exchanger,

each of said fins having a corrugated pattern over sub stantially theentire area thereof and including continuous corrugations extendingbetween adjacent openings extending radially from said adjacent openingsand having substantially the same shapes and arrangement as the magneticlines of force between unlike magnetic poles.

References Cited by the Examiner UNITED STATES PATENTS 1/1905 Humphrey.10/ 1925 Modine.

1/1933 Caldwell 165-182 X N. R. WILSON, Assistant Examiner.

1. A HEAT EXCHANGER COMPRISING A PLURALITY OF SPACED FINS EACH INCLUDINGOPENINGS FOR RECEIVING THE TUBE COMPONENTS OF SAID HEAT EXCHANGER, SAIDOPENINGS BEING POSITIONED SO THAT EACH SET OF FOUR OPENINGS FORM THEFOUR CORNERS OF A RECTANGLE, EACH OF SAID FINS HAVING A REPETITIVEPATTERN OF CORRUGATIONS OVER SUBSTANTIALLY THE ENTIRE AREA THEREOF, AUNIT PATTERN OF SAID CORRUGATIONS BEING DEFINED BY SAID RECTANGLE, SAIDUNIT PATTERN OF SAID CORRUGATIONS BEING DEFINED BY TENDING RADIALLY FROMEACH OF SAID OPENINGS AND TERMINATING IN AN ADJACENT OPENING.